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2019 American Chemical Society. Polar polymers like poly(N-isopropylacrylamide) are insoluble in nonpolar solvents. This work shows how hydrogen-bond solubilization can be used to generate chemically reversible responsive solubility of a polar polymer like PNIPAM in nonpolar solvents. This was accomplished by adding hydrogen-bonding carboxylic acids like acetic, pentanoic, octanoic, and oleic acids to a suspension of PNIPAM in solvents like alkanes and toluene. The results showed that the PNIPAM solubilization depends on the solvent used and on the size of the alkyl group in the carboxylic acid. Once solubilized, PNIPAM can be quantitatively precipitated from alkanes or toluene either by addition of a base or a hydrogen-bond competitor to form a biphasic liquid solid mixture of the nonpolar hydrocarbon solvent and PNIPAM polymer as a solid. When a PNIPAM-bound rhodium catalyst was prepared, this same chemically reversible responsive solubility served to generate a homogeneous hydrogenation catalyst from an insoluble polymeric catalyst. This catalyst's activity was comparable to that of a low molecular weight catalyst, but the polymeric catalyst was successfully recoverable and recyclable through four cycles of dissolution/precipitation in toluene, chemistry that could be expanded to include other molecular recognition chemistry and used to prepare other sorts of recyclable catalysts
Industrial & Engineering Chemistry Research
author list (cited authors)
Fu, Y., Perales, C., Eliason, T., & Bergbreiter, D. E.